A Comparison Of Different Insect Communities Biology Essay

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One of several fairly undeniable overviews in community ecology is a latitudinal gradient of increase in biological species richness and diversity from the temperate regions to the tropics (Krebs 1985). It is also equally undeniable, however, that most tropical organisms are poorly studied and the little that is known about any group of organisms comes largely from studies of temperate species (Gadagkar et al. 1990).

Plants, birds and mammals are the best-known and best-studied components of tropical rain forests, but they make up only a tiny fraction of the total number of species- probably less than 1%. Invertebrates are the dominant animals of the rain forest, contributing most of the species and the overwhelming majority of individuals (Primack 2002). Of all invertebrates, the insects contribute most of the biomass and probably most of the species although in contrast to the plants, birds, and mammals, where most species have already been described and named by scientists, rain forest insects are much less known (Primack 2005).

Even though many rain forest insect groups are very poorly known, there are some significant exceptions including such orders as: Lepidoptera (moths and butterflies), Diptera (flies), Hymenoptera (bees, wasps etc), Coleoptera (beetles), Hemiptera (true bugs) and Orthoptera (crockets, grasshoppers). All of the above excluding the latter group are considered as the majority of species inhabiting tropics.

There are many examples of fluctuation patterns of insect populations. A great compilation is summarised by Itŏ (1980). For the rainforests, however, such data are particularly limited (Wolda 1983). Despite the data maintained by Bigger (1976) data for insects available in print are practically absent which may be due to the lack of appropriate research methodology (Gadagkar et al. 1990). There is no data in the literature on insects in an undisturbed tropical forest (Wolda 1983). Nonetheless, these data are greatly applicable to population dynamical hypotheses. Main characteristics of rainforests are a species abundance and a climatic stability, at least when consider temperature, unmatched in all but several temperate habitats. These two aspects highly donated to a common idea that in rainforests insect populations ought to be more constant and less fluctuating, than similar populations in other locations (Orians 1975).

Many research have suggested that tropical insects experience seasonal fluctuation in abundance, at least for those areas of rainforests where wet and dry periods rotate (Wolda 1977). In general, parts of tropics with a dry season show much lower insect richness than areas where a wet season occurs. It appears possible that the occurrence of seasons and abundance of insects is related. It is suggested that insect richness depends on seasonal presence of its food, which fluctuates due to seasonality.

According to Janzen and Schoener (1967) adjacent tropical communities can have greatly different insect components. It is most likely due to the variation of vertebrate predation and plant availability among insect communities. When these findings were compared with temperate habitat insect communities the tropical communities showed much higher diversity and abundance of insect species and most likely a greater internal uniqueness than similar temperate communities (Janzen and Schoener 1967).

The aim of this exercise was to find out whether there are differences in community composition between two sites (Kula Belalong and Tasek Merimbun), and whether there were differences within sites between the forest samples, the river samples (Kuala Belalong) and the samples taken from the open area near the drive (Tasek Merimbun) (Knell 2009).

Methodology:

Location and performance:

This exercise was carried out to give an idea of the community composition of the flying insects at Tasek Merimbun and Kuala Belalong. The data that was collected was from light traps (4 in Tasek Merimbun: 2 sets on the driveway- disturbed area, 2 sets in the forest- calmer area; another 4 in Kuala Belalong: 2 sets in the forest, 2 sets by the river) and from Malaise traps (4 in each- Tasek Merimbun and Kuala Belalong; the location of the traps the same as in a case of light traps). The former is count data only at the order level, the latter data is divided into morphospecies counts (Knell, 2009).The location of setting up the traps was not random and it meant to indicate the variation, species abundance and insect preferences in terms of choosing their occurrence.

The traps were left overnight in indicated regions and were collected the following day.

Equipment used:

A light traps were much easier to maintained and used. Simply, it was made from a funnel, a round gallon can and a light. The funnel was placed on the can (Fig.1), and the light was suspended slightly above the funnel. Insects that fly into the light bulb fell down the funnel and were trapped in the can. The spout of the funnel should be large enough to let the insects drop through it easily, but not so large as to let the insects fly out again. A few strips of one inch wide newspaper in the can had to be provided to give insects a place to hide so they were less likely to try to escape. When getting the insects out of the trap, the can and funnel had to be put together into the collection net before removing the funnel. This prevented active insects from escaping.

Light Trap Figure : A simplified sketch of a light trap

On the other hand, a Malaise trap is a large, tent-like structure with a big opening at the bottom for insects to fly into and a tall central wall that directs the flying insects upwards to a cylinder containing a killing agent [5]; for the purpose of this experiment the killing agent was ethanol. Here, ethanol damaged some flying insects like Lepidopterans but, conversely, it kept the specimens preserved for a longer period of time.

http://www.inhs.uiuc.edu/cwe/wwwtest/collect/HTML/g16.gif

Figure : A simplified illustration of Malaise trap with indications of collecting jar and mesh netting

Results:

A summary of the insect catch data in the form of the number of orders, families, morphospiecies and individuals for each of the sites are shown in Table 1. In any given site it was recorded from 2-5 orders, 5-23 morphospecies and 6-46 individuals. In all the 8 sites put together it was recorded that they contained 5 orders and 198 individuals. Some patterns in this data are instantly evident. The highest number of individuals, morphospecies and the highest diversity were observed in Tasek Merimbun (drive 1) and Kuala Belalong (river 1), while the lowest number of individuals, morphospecies and the lowest diversity were observed Tasek Merimbun (drive 2).

Insect Community in Tasek Merimbun and Kuala Belalong (Malaise traps)

When comparing two rank-abundance histograms from two sites (Tasek Merimbun and Kuala Belalong) (Fig. 3 and 4) the first noticeable difference is in morphospecies abundance. In Tasek Merimbun each of the order is much more variable.

In Kuala Belalong only Hymenoptera and Lepidoptera have more than two morphospecies, the rest of the orders have either one or two morphospecies. The most abundant orders in Kuala Belalong were again Lepidoptera (river 2) - 4 morphospecies with 21 individuals in total and Hymenoptera (river 1) - 9 morphospecies with 21 individuals in total (Fig. 3). Lepidoptera collected in both forest regions in Kuala Belalong is also fairly abundant- 6 morphospecies with 14 individuals (forest 1) and 9 morphospecies with 12 individuals (forest 2). The rest of the groups including Coleoptera, Bugs and Orthoptera do not play a significant role since their abundance varies between 0 to 11 individuals occurring, at most, in two morphospecies.

Orders in Tasek Merimbun are much more diverse. The most abundant is again Lepidoptera (forest 2) - 5 morphospecies with 23 individuals (Fig.4). On the other hand, Lepidoptera in a forest 1 area has 12 individuals which are spread over 10 different morphospecies. Interestingly, drive 2 and forest 1 regions did not have any Lepidoptera individuals recorded. In a case of Hymenoptera- second most abundant order occurred in 3 regions- forest 1 and 2, and drive 1; in drive 2 there was no individuals recorded. The most abundant is forest 1- 4 morphospecies with 15 individuals and drive 1 area- 7 morphospecies with 8 individuals. The rest of the orders are not of mayor interest since their appearance varies between 0 and 4 individuals per site.

Insect Community in Tasek Merimbun and Kuala Belalong (Light traps)

Comparing two sites (Tasek Merimbun and Kuala Belalong), yet again, more variable and diverse is Tasek Merimbun (Fig. 5 and 6). Tasek Merimbun area has 3 major samples of caught insects. They are as follow: Hymenoptera, drive 1 (34 individuals); Lepidoptera, forest 2 (32 individuals) and Hymenoptera, forest 1 (29 individuals). Also Hymenoptera in forest 2 was pretty abundant reaching 18 insects and Lepidoptera in drive 2 indicating 14 individuals (Fig. 5).

Conversely, when considering abundance, Kuala Belalong region is definitely superior over Tasek Merimbun. The highest number of individuals is recorded for Hymenoptera (river 1) with 120 catches (Fig. 6). Apart from that, remain orders are not that abundant and the number of collected insects fluctuates between 0 to 42 individuals (Fig.6).

Diptera Abundance in Tasek Merimbun and Kuala Belalong (Malaise traps)

When considering two forest areas from two sites (Tasek Merimbun and Kuala Belalong) the difference is immediately apparent. Forest area in Tasek Merimbun showed greater richness of Diptera order than a forest of Kuala Belalong. Tasek Merimbun: forest 1- 6 morphospecies 103 individuals; forest 2- 6 morphospecies 128 individuals (Fig. 7), whereas Kuala Belalong: forest 1- 4 morphospecies 36 individuals; forest 2- 3 morphospecies, 56 individuals (Fig. 8).

River areas in Kuala Belalong were very abundant and diverse. River 1 indicated 24 morphospecies with 167 individuals and river 2 illustrated 7 morphospecies with 62 individuals collected (Fig. 8).

Drive sites in Tasek Merimbun were not especially diverse and abundant indicating 8 morphospecies with 48 individuals (drive 1) and 5 morphospecies with 30 individuals (drive 2) (Fig. 7).

Diptera Abundance in Tasek Merimbun and Kuala Belalong (Light traps)

Abundance of Diptera between two sites (Kuala Belalong and Tasek Merimbun) varied greatly. In Tasek Merimbun two areas (drive 2 and forest 2) indicated that the number of caught Diptera was over 1000 individuals (Fig. 9), whereas in Kuala Belalong the highest number was just over 200 individuals (Fig. 10). Apart from that, in Tasek Merimbun there were 200 individuals collected (drive 1) and 0 (forest 1) (Fig. 9). In Kuala Belalong forest 1 area showed 35 individuals found and the remaining two had 9 and 11 individuals in forest 2 and river 2 respectively (Fig. 10).

site

No. of orders

No. of morphospp.

No. of individuals

Tasek Merimbun

 

 

 

Drive 1

4

23

28

Drive 2

2

6

6

Forest 1

2

5

17

Forest 2

3

10

29

total

 

 

80

Kuala Belalong

 

 

 

River 1

5

16

46

River 2

5

11

40

Forest 1

2

7

16

Forest 2

3

11

16

total

 

 

118

Table : Summary of catch data

Discussion:

Tropics are a great example of biodiversity. There is a high diversity of different plants, invertebrates and vertebrates which to survive and get the most of survival ought to cooperate. The above study focused only on invertebrates particularly insects, their abundance in the rain forest and the difference that could appear between different sites within tropics.

Because of the low amount of recorded samples and the requirement to contain all collected insect species in any analysis, it was best to use at least a couple of different trapping methods so as to catch variety sorts of insects. The findings showed that the catches for the two methods are rather diverse from each other. The low amount of sampling and hence the resulting small number of insect caught in each trap (except Diptera) lead to random fluctuations. It would be necessary to repeat the experiment using several traps of the same sort in each habitat site. It might reveal that the insect caught by the same method have greater similarity to each other rather than to insects caught by other methods. Further, the insect caught in different replicate traps of a site have a greater similarity to each other rather than to insects caught in some other site.

In overall, the Tasek Merimbun and Kuala Belalong sites formed two different clusters, suggesting that geographical separation and altitudinal variation reverse even extreme differences in levels of interruption.

Light traps

Diversity of collected insects shaped as follow: Diptera, Hymenoptera, Lepidoptera, and Coleoptera; where the most abundant was order Diptera. The main reason of this might be due to the type of traps used, which were design to catch mainly flying insects rather than terrestrial organisms. Consequently, there were no millipedes found in both sites (Kuala Belalong and Tasek Merimbun) and Coleoptera which according to many literature sources (White 1983; Corlette 2009) ought to be the most diverse order in the rain forests was in minority. One explanation why Coleoptera was not abundant species in light traps is that the beetles might not come close enough to the traps. If the light traps were put higher in the canopy the results might have been entirely different indicating domination by Coleoptera. Also, it could depend on the species of Coleoptera as some do not fly around that often whereas others are found only in the canopy.

A very high number of Diptera created a fly 'dust' (all cases except forest 2 in Tasek Merimbun). One indication suggests that it, yet again, might be caused by the type of traps used during the experiment as well as the location chosen.

Order Lepidoptera is highly associated with plants. Because butterflies and moths tend to eat a lot of flora the expectation would be to see plenty of insects in the forest. From the data gathered it has been clearly proven (Fig. 3, 4, 5). Further, high populations of Lepidoptera species are more likely to occur in plants older than five years and especially during the rainy season (October-March) (Guedes 1999). An abundance structure, namely- Diptera, Hymenoptera, Lepidoptera and Coleoptera makes a perfect sense. Traps located on the driveways in Tasek Merimbun were further from the lake, but in Kuala Belalong they were set up right next to the river. These geographical locations might be great indicators of higher abundance of flies in certain locations over others. In a case of Kuala Belalong flies were stopped from flying to the forest site because of the steeps separating the river and forest.

Malaise traps

According to rank-abundance charts (Fig. 7 and 8) some of the species of Diptera outnumbered the other orders. Whereas Diptera community in the forest in Kuala Belalong was not abundant, it showed fairly even shape in the river. In Tasek Merimbun, however, some regions were dominated and outnumbered (especially forest 1 and 2) and, in general, the Diptera community was even.

Other orders with high abundance were Lepidoptera as well as Hymenoptera. Here, once more, as in light traps the interpretation may be similar: type of traps and their location as the main key. The latter community was even in each site, showing everywhere a reasonable number of individuals as well as morphospecies. One concern may arise when referring to last year where the number of Hymenoptera insects was much greater, thus illustrating a massive drop this year.

As mentioned previously, Coleoptera is one of the most abundant species in the tropics. From the data provided there were only a few species recorded, most of them represented by only 1 individual. Nevertheless, the community was stable and even in overall. This structure might be caused by location of the traps which when higher up in the canopy could show different results.

An additional problem arises when considering number of morphospecies between Tasek Merimbun and Kuala Belalong. In Tasek Merimbun the traps were on a driveway and in the forest thus more open and disturbed area versus sheltered and calmer area. In Kuala Belalong the locations of traps were different too- river (open, more disturbed area) and forest (closed, calmer area). This might have had an impact into an insect community in these two locations. Also, the climate could have played a major role since in Tasek Merimbun it was much less humid than in Kuala Belalong. It can indicate differences in caught insects, numbers of morphospecies and their individuals.

In conclusion, the communities were very similar in overall with an obvious domination of Diptera species (the only exception forest 1 in Tasek Merimbun; Fig. 9). All communities show what is expected in tropic forests, which is diversity and evenness. There were two exceptions to that. Firstly, there was a lack of Diptera order in forest 1 in Tasek Merimbun and secondly Coleoptera order did not show expected richness in general.

Here, is also important to make a point about diversity and evenness of tropics versus temperate forests. The main difference between both is that the temperate forests will not be high diverse and abundant and moreover, the evenness also will not be apparent. That is why it is so important to keep checking on tropics to make sure all propulsions are kept to save as much of it as it possibly can be.

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